1. Field of the Invention
This invention relates generally to nuclear reactors, and more particularly to determining standardized rod types applicable to a plurality of different fuel bundles in cores of different nuclear reactors.
2. Description of the Related Art
A core of a nuclear reactor such as boiling water reactor (BWR) or pressurized water reactor (PWR) has several hundred individual fuel bundles of fuel rods (BWR) or groups of fuel rods (PWR) that have different characteristics. These bundles (or fuel rod groups) are preferably arranged so that interaction between rods within a fuel bundle, and between fuel bundles satisfies all regulatory and reactor design constraints, including governmental and customer-specified constraints. Additionally for a BWR, the control mechanisms, e.g. rod pattern design and core flow, must be determined so as to optimize core cycle energy. Core cycle energy is the amount of energy that a reactor core generates before the core needs to be refreshed with new fuel elements, such as is done at an outage.
In the case of a BWR, for example, the number of potential fuel bundle arrangements within the core and individual fuel rod types within a bundle may be in excess of several hundred factorial. From these many different possible configurations, only a small percentage of fuel rod types may satisfy all applicable design constraints for a particular core of a nuclear reactor. Further, only a small percentage of these fuel rod types, which do satisfy all applicable design constraints, are economical. Conventionally, a typical fuel bundle useable in a BWR core may include between about 10-30+ different rod types therein. This is undesirable, in that the greater the number of different rods types, the greater the manufacturing complexities and cost, which may result in higher bundle costs to the consumer.
Traditionally, rod pattern, fuel bundle and/or core design determinations have been made on a trial and error basis. Specifically, and based on only the past experience of the engineer or designer, in designing a particular design an initial design was identified. The initially identified design, such as a particular fuel bundle design for a core, was then simulated in a virtual core by computer. If a particular design constraint was not satisfied, then the arrangement was modified and another computer simulation was run. Many weeks of resources typically were required before an appropriate design was identified using the above-described procedure.
For example, one conventional process being used is a stand-alone manual process that requires a designer to repeatedly enter reactor plant specific operational parameters into an ASCII text file, which may serve as an input file. Data entered into the input file may include the configuration of fresh and exposed fuel bundle placements, blade notch positions of control blades (if the evaluated reactor is a boiling water reactor (BWR)), soluble boric acid concentration (if a PWR, for example), core flow, core exposure (e.g., the amount of burn in a core energy cycle, measured in mega-watt days per short ton(MWD/st), etc.
A Nuclear Regulatory Commission (NRC) licensed core simulation program, which may be embodied as a software program running on a suitable computer, for example, reads the resulting input file and outputs the results of the simulation to a text or binary file. A designer then evaluates the simulation output to determine if the design criteria have been met, and also to verify that no violations of margins to thermal limits have occurred. Failure to meet design criteria (i.e., violations of one or more limits) requires a manual designer modification to the input file. Specifically, the designer would manually change one or more operational parameter(s) and rerun the core simulation program. This process may be repeated until a satisfactory design was achieved.
This process is extremely time consuming. The required ASCII text files are laborious to construct, and often are error prone. The files are fixed-format and extremely long, sometimes exceeding five thousand or more lines of code. A single error in the file results in a crash of the simulator, or worse, results in a mildly errant result that may be hard to initially detect, but will profligate with time and iterations to perhaps reduce core cycle energy when placed in an actual operating nuclear reactor core. Additionally, no assistance is provided via the manual iterative process in order to guide a designer toward a more favorable solution. In the current process, the responsible designer or engineer's experience and intuition are the sole means of determining a design solution.
There is believed to be no process developed which can effectively design fuel bundles that are useful over a wide range of nuclear reactors (or different reactor designs at different plant sites), and which satisfies multiple core constraints or design parameters for each of the different reactors. Further, there is believed to be no known automated process to determine a given, standardized set of rod types for building fuel bundles that may be applicable to many different nuclear reactors.